1974 Dart Sport 489 Differential Question

Transmission and Drivetrain Tech

  1. Warren

    Warren Active Member

    Messages:
    35
    Likes Received:
    1
    Joined:
    Dec 30, 2009
    Local Time:
    1:20 AM
    Hello, my Hang 10 purchased used came with the dealer sticker and originally was a 318 with a 3.23 axle ratio. It now has a 360 and a 8.75 489 differential case. According to my factory manual, 1974 Darts did not have the 8.75 available so my question is:

    Is my 8.75 489 case a retrofit or were there some 1974's supplied with the 8.75 489 from the factory?

    Thanks.
     
  2. partsman1965

    partsman1965 Well-Known Member

    Messages:
    444
    Likes Received:
    46
    Joined:
    Jul 16, 2013
    Location:
    Bourbonnais, Illinois
    Local Time:
    1:20 AM
    74 318 should have been 8.25..does the 8.75 have large bolt pattern?? I'd bet it was from earlier year? I have a 74 with 1970 8.75 but it still has small bolt pattern.
     
  3. OldmanRick

    OldmanRick Well-Known Member

    Messages:
    7,097
    Likes Received:
    318
    Joined:
    May 11, 2012
    Location:
    Ladson, Sc
    Local Time:
    2:20 AM
    Yes...^^^^^....Never seen a 74' A body with a 8.75. And a ratio in that range would have been a 3.21 with a 8.25. It would be interesting though if it was by chance a dealer installed rear? Just be glad you have what you have.....You're $$$ ahead of the game. :thumbrig:
     
  4. 74DartSwinger360

    74DartSwinger360 The Brat Pack

    Messages:
    4,651
    Likes Received:
    113
    Joined:
    Apr 16, 2012
    Location:
    Valrico, Florida
    Local Time:
    2:20 AM
    No A Body after 72 ever had a factory installed 8 3/4 this was also the same year they got rid of Small Bolt Pattern. (except some 73 Slant 6 Stripper cars which had 4 wheel drums)
    So If it is Big Bolt Pattern the axels were swaped or drilled out

    1974 with a slant 6 or 318 would have been a 7 1/4 or 8 1/4 from the factory
    8 1/4 being an added cost option
     
  5. Warren

    Warren Active Member

    Messages:
    35
    Likes Received:
    1
    Joined:
    Dec 30, 2009
    Local Time:
    1:20 AM
    Thanks everyone for the info. Yes the axles are the big bolt pattern as have the original Rallye wheels with largeacorn center caps. I did find a receipt where the axle stud plates were welded up and re-drilled by Moser in 1993 so I assume the axles are not original. I have a lot of receipts of this car but no info on the differential other than a 4.10 ratio gears installed in 2000. I have since replaced that with a 2.94 for better economy and hiway cruising.
     
  6. SGBARRACUDA

    SGBARRACUDA ROY FABO Gold Member

    Messages:
    16,972
    Likes Received:
    5699
    Joined:
    Dec 7, 2006
    Location:
    PLANT CITY FL. and PERRY GA.
    Local Time:
    2:20 AM
    If the small bolt pattern axles were re drilled then they would have had to re drill the brake drums also. The A-body 8 3/4 small bolt rear used a axle offset specific to this rear end. Are the drums drilled also?
     
  7. cosgig

    cosgig MoBro Inc. FABO Gold Member

    Messages:
    11,281
    Likes Received:
    4395
    Joined:
    Jul 20, 2008
    Location:
    Pinckney, Michigan
    Local Time:
    1:20 AM
    Also, NO A-body 8 3/4" ever came with anything other than the small bolt pattern!
     
  8. Warren

    Warren Active Member

    Messages:
    35
    Likes Received:
    1
    Joined:
    Dec 30, 2009
    Local Time:
    1:20 AM
    Sgbarracuda:
    I am not sure the brake drums were drilled (or just replaced) but my memory says there is a 5 hole drilled spacer plate between the drum and axle (I would have to remove a wheel to confirm).
     
  1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.